[bldg-sim] need a reality check for modeling fan energy of a 100% CV reheat system

[Jeff Haberl]

Tom. 

You can do a simple cross-check with ASHRAE's 865-RP accuracy test, which includes system and zonal fan energies at varying delta-P. Spreadsheets used for the 865-RP systems, including CVReheat systems are available via the ESL's website. 

Jeff


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Jeff S. Haberl, Ph.D., P.E.............................jhaberl at esl.tamu.edu

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-----Original Message-----
From: bldg-sim at gard.com
To: bldg-sim at gard.com
Sent: Sat Jun 03 22:10:17 2006
Subject: [bldg-sim] need a reality check for modeling fan energy of a 100% CV reheat system

Hello everyone:
 
I'm modeling a 400,000 sf hospital with 100% outside air and constant volume reheat system. The priority is infection control and not energy savings, so the total ventilation load is HUGE. 
 
Here's my question. I've input all the CFM values for each supply air handler (about 500,000 cfm combined), but -- strictly speaking -- there is no return air since all air is exhausted. So, how do I account for the kWh of all the exhaust air handlers? The exhaust air handlers run about 2/3 the CFM of the supply air, with the difference made up by exfiltration and a multitude of special-purpose exhaust fans (in the labs and so on).
 
I figure my only real option is to treat the exhaust air handlers as electric loads in the building. They don't contribute to the heating and cooling loads, but they are a significant energy use.
 
Can you think of an alternate way to model exhaust air fans to account for their energy use while eliminating any energy use for return fans?
 
...Tom
 
 
Thomas J. White, P.E.
Associate
Lead Engineer, Energy Services
LEED® Accredited Professional

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